1. Field of the Invention
The invention relates to air compression systems and more particularly, to a pressure amplifying pneumatic pump system operating off of air pumped by a non-firing cylinder of an internal combustion engine.
2. Description of the Problem
Designers of internal combustion engines have long appreciated that such engines can function as air pumps. For example, U.S. Pat. No. 3,365,014 to Clingerman describes a multi-cylinder diesel engine adapted to operate as a self-powered air compressor. This engine provides for shutting off the flow of fuel to a bank of cylinders and then diverting the air pumped by the cylinders to an auxiliary outlet for use. The cylinders continuing to receive fuel power the vehicle and the air pumping cylinders. The compressed air made available can be used to operate auxiliary equipment on the vehicle.
An example of an opportunity to recapture kinetic energy of a vehicle which is otherwise lost during braking would be to use the engine as a pump to compress air. Engine compression braking has long been used as an auxiliary braking system on diesel engine equipped trucks. An example of such a system is the widely used Jepsen engine brake. Engine compression braking operates by cutting off fuel to the cylinders and coupling the vehicle""s momentum back to the pistons through the drive shaft. The cylinders"" intake valves operate to allow air to be drawn for compression strokes, but the cylinders"" exhaust valves are opened at or just before top dead center (TDC) of the pistons"" cycles to exhaust the compressed air. The energy expended to compress the air in the cylinders is lost through the exhaust and no rebound energy is returned to the crankshaft through the pistons during the expansion portions of the piston strokes. In this way a substantial portion of an engine""s rated power can be applied to braking. An engine incorporating engine compression braking would seem well adapted for operating as an engine pump to recover a proportion of vehicle energy otherwise wasted during braking.
Unfortunately, diverting engine cylinders for use as air compression pumps provides relatively little practical pressure gain. A non-firing cylinder in a diesel engine reliably generates a pressure of about 200 psi and can, under some circumstances, develop 300 psi. Absent modification of the cylinder not even these limited pressures are available for use though. The air typically must be released to some portion of the exhaust system, resulting in a substantial pressure drop. Assuming diversion of the air using a butterfly valve and check valve positioned as close to the exhaust valve from the cylinder as practical, an exhausted air pressure of perhaps 100 psi will be generated. Such low pressures have worked against using the engine itself an air compressor.
As a consequence, pressurized air is usually provided from an auxiliary pump driven by a belt off of the engine. Unless the pump is clutched, this arrangement constitutes a parasitic drag on the engine and has been criticized for this reason. If the system is clutched it adds weight and complexity to the vehicle. Baguelin, U.S. Pat. No. 4,492,192, proposed modifying one cylinder of a diesel engine to introduce an extra valve as an outlet for compressed air to make the cylinder more effective as an air pump. Such a cylinder, while achieving better pressures than 100 psi, is still limited by the compression ratio of the engine. It is also possible to couple air pumps to the vehicle wheels with clutches to provide kinetic energy recapture during braking. These proposals are mechanically complex.
One object of the invention is to improve the efficiency of motor vehicles equipped with internal combustion engines.
Another object of the invention is to provide an engine driven, high pressure air compression system for use on a motor vehicle.
Still another object of the invention is to eliminate the need for auxiliary, belt driven air compressors.
Yet another object of the invention is to provide a vehicle braking system providing energy recovery.
Another object of the invention is to reduce the need for stored vehicle electrical power.
The invention provides for these and other objects with an engine exhaust driven fluidic amplifier which operates as a high pressure air pump. The engine is preferably a multi-cylinder diesel engine which can be operated in a split mode with one or more cylinders diverted to operation as first stage air compressors. Cylinders operate as air compressors upon cut off of fuel injection to the cylinders. Air exhausted from one or more of the cylinders can be applied by selective positioning of an escape valve as an input to one or more pneumatic amplifiers. The pneumatic amplifiers draw air from the environment and compress the air by a substantial amount over the pressure of the air exhausted from the engine. The output of the pneumatic amplifiers is delivered to a high pressure storage tank. A pneumatic amplifier comprises a shuttle piston having a large area piston head exposed to the exhaust chamber and a small area head exposed to a compression or pumping chamber. A check valve passes air from the pumping chamber to the pressure tank. The fluidic amplifier allows pressurization of a storage tank to levels of 1600 to 1800 psi or higher. Air compressor operation is triggered by reduced air pressure in the storage tank occurring concurrently with the engine operating at a low or negative load.
Additional effects, features and advantages will be apparent in the written description that follows.